1. Field of the Invention
This invention relates a liquid catalyst component, a catalyst system containing said catalyst component for copolymerization of ethylene with .alpha.-olefins and a process for producing ethylene-.alpha.-olefin copolymers using said catalyst system, and more particularly to a process for producing ethylene-.alpha.-olefin copolymers excellent in structural randomness, weather resistance, color protection, corrosion resistance, low temperature property and dynamic property by the use of said novel catalyst system.
2. Description of the Prior Art
As a general process for producing ethylene-.alpha.-olefin copolymers, the process using a catalyst consisting of a compound of transition metal belonging to Group IV to VI of the periodic table and an organometallic compound of a metal belonging to Group I to III of the periodic table, i.e. the so-called Ziegler-Natta catalyst, is widely known.
On the other hand, ethylene-.alpha.-olefin copolymers are requested to have a narrow composition distribution from the viewpoint of practical properties. Thus, in the industry, they are produced by the use of a catalyst system consisting of a vanadium compound such as VCl.sub.3, VOCl.sub.3, VO(OR).sub.3 or the like and an alkylaluminum halide such as Et.sub.3 Al.sub.2 Cl.sub.3 or the like.
However, although the ethylene-.alpha.-olefin copolymers produced with the above-mentioned catalyst system are narrow in composition distribution, the process is low in productivity because the catalyst has a low polymerization activity at high temperatures. Further, this process has problems that the residual vanadium and chlorine cause coloration of the resulting polymer, deteriorate its weather resistance and promote its corrosion. Accordingly, ashes must be thoroughly eliminated from the polymer in order to prevent these problems.
Further, the process using the above-mentioned catalyst system is disadvantageous in that, if ethylene and higher .alpha.-olefin are copolymerized with the catalyst system, the resulting copolymer is very low in molecular weight and cannot have a satisfactory mechanical strength, and in addition catalyst activity is very low.
In view of the above-mentioned circumstance, a process using a catalyst system consisting of a titanium compound or a zirconium compound and an aluminum compound has been disclosed, and recently a process using a catalyst system consisting of a titanium compound or a zirconium compound and aluminoxane has been proposed.
However, the ethylene-.alpha.-olefin copolymers produced with these catalyst systems have a low molecular weight, and they cannot be said to be satisfactory from the viewpoint of practical properties.
On the other hand, as a process for polymerizing or copolymerizing olefins by the use of a catalyst system consisting of a compound having titanium-nitrogen bond and an organoaluminum compound, there have been disclosed a process for polymerizing ethylene with a catalyst system consisting of an organoaluminum compound and a solid component prepared by supporting a titanium amide compound or an alkali metal salt of titanium amide compound on magnesium halide (DE-OS 2,030,753), a process for copolymerizing ethylene and .alpha.-olefin with a catalyst system consisting of aluminoxane and a titanium amide compound having .pi.-allyl ligand [Japanese Patent Application Kokai (Laid-Open) No. 62-121708], a process for polymerizing ethylene or copolymerizing ethylene and .alpha.-olefin with a catalyst system consisting of a titanium diphenylamide compound and an organoaluminum compound (EP-A-0 104 374), a process for polymerizing .alpha.-olefin or copolymerizing ethylene and .alpha.-olefin with a catalyst system consisting of a titanium amide compound having an aryl substituent and an organoaluminum compound (Japanese Patent Publication No. 42-22691), a process for homopolymerizing ethylene or .alpha.-olefin or copolymerizing ethylene and .alpha.-olefin with a catalyst system consisting of an organoaluminum compound and a lower alkyl group-containing titanium amide compound such as diethylamido-titanium trichloride and the like [Japanese Patent Publication No. 41-5379; J. Polymer Sci., Part A-1, 241, 6 (1968)], a process for polymerizing ethylene with a catalyst system consisting of tetrakisdiphenylamido-titanium and an organoaluminum compound (Japanese Patent Publication No. 42-11646), etc.
However, when applied to the copolymerization of ethylene and .alpha.-olefin, all the catalyst systems disclosed in the above-mentioned references are disadvantageous in the following points. Thus, the process of DE-OS 2,030,753 is disadvantageous in that the resulting ethylene-.alpha.-olefin copolymer has a broad composition distribution; the process of Japanese Patent Application Kokai (Laid-Open) No. 62-121708 is disadvantageous in that the resulting copolymer has a low molecular weight; and the processes of EP-A-O 104 374, Japanese Patent Publication No. 41-5379, Japanese Patent Publication No. 42-22691 and J. Polymer Sci., Part A-1, 241, 6 (1968) are disadvantageous in that composition distribution of the resulting copolymer is yet unsatisfactory in narrowness. Further, the process of Japanese Patent Publication No. 42-11646 is disadvantageous in that the resulting copolymer is yet unsatisfactory in narrowness of composition distribution and the catalyst is insufficient in activity.